Technology exists for routing communications made from a wireless handheld telephony device through a server, such as an enterprise or other type of call control server. This can be done, for example, to make it appear as if a communication originated from a user's place of business or to prevent a party receiving the communication from accessing the wireless user's wireless number. Using some protocols, such as the Dual Mode Transfer (DTM) protocol, wireless communications may use multiple communications paths, including for example both an audio/voice path for relaying a voice communication and a data path for sending data such as, for example, control information between the server and the wireless handheld telephony device.
For example, a server may send a control command to a wireless handheld telephony device informing it of an incoming communication intended for delivery to the wireless device. Similarly, the wireless handheld telephony device may send a control command to the server, for example, indicating that an incoming communication should be accepted, or requesting that a current communication process be put on hold. Communication which is sent using the same path as voice communications, for example an audio path, may be referred to as in-band communication. Communication through some other means, such as through a data path, may be referred to as out-of-band communication.
A data path, or channel, may be faster and more reliable than an audio path or channel. For this reason, data, such as control commands, would normally be sent via the data path when a data path is available. In some situations, however, the data connection between the wireless handheld telephony device and the server may be lost during an ongoing communication. For example, wireless handheld telephony device may roam to a tower of a wireless network which does support a dual path protocol (i.e. a protocol involving both a data and non-data or audio path), such as 3G protocols (e.g. CDMA2000 1x EV-DO or UTMS), to a tower of a wireless network which does not support the dual path protocol, such as 2G protocols without DTM (e.g. GSM/GPRS). It is also possible for a data path which was previously lost or unavailable to become available, for example, if the wireless handheld telephony device roams to tower or network which supports the dual path protocol.
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